1. Field of the Invention
The present invention relates to a charged particle beam drawing apparatus for directly drawing a pattern onto a sample wafer using a charged particle beam such as an electron beam, and, in particular, a charged particle beam drawing method for drawing a repeating pattern, such as a cell array pattern, by a partial blank drawing method.
This application is based on Japanese Patent Application No. Hei 11-294718, the contents of which are incorporated herein by reference.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
A blank drawing method is used as an example of an electron beam drawing method for lithography in a process for preparing a capacity contact in a DRAM manufacturing process, or the like. In this method, when the same patterns are sequential, a part of the repeating pattern is provided as a cell projection exposure aperture on the second mask (which is also called xe2x80x9cthe second aperturexe2x80x9d), the electron beam penetrates the first mask (which is also called xe2x80x9cthe first aperturexe2x80x9d) on which a rectangular hole is provided, and the electron beam penetrates the second mask having the cell projection exposure aperture. As a result, plural patterns are simultaneously drawn on a sample wafer. That is to say, the blank drawing method is executed so that the electron beam penetrates the cell projection exposure aperture on the second mask, wherein the area of the cell projection exposure aperture of the second mask is the same as an irradiation area of the electron beam which has already penetrated the rectangular hole on the first mask, as a result, the cell projection exposure aperture pattern formed on the second mask is sequentially drawn on the sample wafer. This method particularly reduces drawing time for periodic patterns.
When a repeating pattern is drawn by the partial blank drawing method, in a preparation step of data of the repeating pattern, a repeating pattern is selected from design data as a basic cell for a partial blank drawing and the repeating pattern is output as partially blank direct drawing data. However, a number of the periodic repeating pattern may not agree with an integer multiple of the number of a pattern of the basic cell for the partial blank drawing. Conventionally, to solve this problem, the partial blank drawing method was controlled as follows:
(1) A size of the basic cell for the partial blank drawing is adjusted and selected not so as to generate an excess pattern.
(2) To improve throughput, a pattern group having a maximum size within an area in which the partial blank drawing can be carried out, is selected as the basic cell for the partial blank drawing. On the other hand, the excess pattern, as a fraction which is generated at the end of a cell array pattern and cannot be in the maximum area is drawn using an aperture of a single pattern provided on the second mask or using a variable rectangular drawing method by combining the pattern of the first mask and the pattern of the second mask.
(3) To improve the throughput, a pattern group having a maximum size within an area in which the partial blank drawing can be carried out is selected as a first basic cell for partial blank drawing. On the other hand, the excess pattern as a fraction which is generated at the end of a cell array pattern and cannot be in the maximum area is selected as a second basic cell for partial blank drawing, an aperture for a partial blank drawing for the excess pattern is provided in addition to an aperture for a main partial blank drawing, and a cell array pattern is drawn using plural type apertures for a partial blank drawing.
FIG. 5 illustrates the above methods (2) and (3). FIG. 5A shows an aperture pattern of the first mask, FIGS. 5B and 5Bxe2x80x2 show aperture patterns of the second mask, and FIG. 5C shows a cell array pattern on a semiconductor wafer to be formed by the cell projection exposure.
As shown in FIG. 5A, a rectangular aperture 12a is provided on the center of the first mask 121. As shown in FIG. 5B, a rectangular aperture 13a and cell projection exposure apertures 13a and 13d to 13g are provided on the second mask 131 which is used in the above method (2). Furthermore, a cell projection exposure aperture 13h is provided on the second mask 132 which is used in the above method (3) for the cell projection exposure aperture 13g having a single pattern on the second mask 131, wherein plural patterns corresponding to an excess pattern are formed on the cell projection exposure aperture 13h. As shown in FIG. 5C, a cell array pattern 11 is composed of a center portion pattern 11a drawn using the cell projection exposure aperture 13b as a standard, and an excess pattern 11b without the center portion pattern 11a. 
In the above method (2), as shown in FIG. 6A, the center portion pattern 11a is drawn using the cell projection exposure aperture 13b on the second mask 131 (a blank shot area 1aa is then shown), and, as shown in FIG. 6B, the excess pattern 11b is drawn one after the other using the cell projection exposure aperture 13g which exposes the single pattern (a blank shot area 1bb is then shown). Furthermore, by combining the rectangular aperture 12a of the first mask 121, and the rectangular 13a of the second mask 131, a rectangular pattern is formed and patterns for the excess pattern 11b are exposed one after the other.
In the above method (3), as shown in FIG. 6A, the center portion pattern 11a is drawn using the cell projection exposure aperture 13b on the second mask 132, and, as shown in FIG. 6Bxe2x80x2, the excess pattern 11b is drawn for each blank shot area 11bc using the cell projection exposure aperture 13h. 
However, when the above method (1) is used, the size of a cell selected as the basic cell for the cell projection exposure is small, therefore, the number of partial blank shots increases and, as a result, the throughput decreases. When the above method (2) is used, since the excess pattern is exposed one after one, the number of partial blank shots also increases and the throughput decreases. When the above method (3) is used, since the throughput is improved, both the cell projection exposure aperture 13b for the center portion pattern and the cell projection exposure aperture 13h for the excess pattern have to be simultaneously prepared on the second mask (wherein a necessary type of cell projection exposure aperture for the excess pattern is not always one), therefore, the number of the cell projection exposure patterns which can be exposed on the second mask, is limited. Normally, the number of pattern types of the cell projection exposure aperture which can be provided on the second mask, is several to dozens.
As a method to solve the above problems, a method in which an excess pattern is drawn by controlling deflection of the electron beam is disclosed in Japanese Unexamined Patent Application, First Publication, No. 7-211609 (Kokai) (which is hereafter called JP 7-211609). FIG. 7 is a schematic diagram showing an overview of the drawing apparatus disclosed in JP 7-211609. The apparatus is composed of an electron beam source 21, an electron beam 22, the first mask 23, a shaping lens 24, a shaping deflector 25, the second mask 26, a reducing lens 27, a locating deflector 28, an objective lens 29, and a semiconductor wafer 30. A cell array pattern 31 composed of the center portion pattern 31a and the excess pattern 31b is drawn on the semiconductor wafer 30.
When the center portion pattern 31a is drawn, the electron beam, after penetrating the first mask 23, is irradiated on all apertures to be exposed. When the excess pattern 31b is drawn, the electron beam, after penetrating the first mask 26, is deflected using the shaping deflector 25 and irradiated on a part of apertures on the second mask 26 to be exposed.
Similarly, the above drawing method is disclosed in Japanese Unexamined Patent Application, First Publication, No. Hei 6-13301 (Kokai).
According to the drawing method disclosed in JP 7-211609, the number of the cell projection exposure apertures which are provided on the second mask, can be decreased. On the other hand, the following problems arise.
The first problem is that it is difficult to place an end portion of the beam at a narrow space between the apertures on the second mask because deflection accuracy of the deflector is not always high. If the end portion of the beam is not placed at the narrow space, an overexposure or an incomplete pattern arises. Insufficient accuracy of the deflector is caused by not perpendicularly crossing the deflecting direction and the electron beam direction, or rotation of the electron beam.
The second problem is that the number of apertures which can be provided on the second mask is limited. Since the exposure of the excess pattern is executed by a positioning shift of the electron beam onto the second mask, not to irradiate to the adjacent aperture by the positioning shift of the electron beam, the interval between the cell projection exposure apertures which is provided on the second mask should be sufficiently wide. As a result, the number of the apertures to be provided on the second mask is limited.
The third problem is that an energy distribution profile is reduced toward the end portion of the irradiation area irradiated by the electron beam. When the electron beam is irradiated onto the mask, the center portion of the irradiation area irradiated by the electron beam is preferably used because the center portion has high energy strength, however, if the apparatus and the method shown in FIG. 7 are used, the end portion of the irradiation area irradiated by the electron beam is used prior to the center portion, so that there is a high possibility that the pattern shape will deteriorate.
An object of the present invention is to obtain a charged particle beam drawing apparatus and a charged particle beam drawing method by which the drawing can be executed with high accuracy so that the number of the cell projection exposure apertures provided on the second mask does not increase and the total number of shots does not increase, by solving problems of the above-mentioned conventional arts.
To achieve the above object, the present invention provides a cell projection exposure-type charged particle beam drawing apparatus, in which a charged particle beam emitted by a charged particle beam source is irradiated for executing cell projection exposure onto a second mask comprising one or a plurality of cell projection exposure apertures through a first mask for exposing the pattern of the cell projection exposure apertures on a sample wafer, wherein the first mask comprises: a main aperture for exposing the whole area of the second mask for the cell projection exposure, and a supplementary aperture having a size of 1/N of the size of the main aperture, wherein N is an integer; and wherein the particle beam drawing apparatus is constituted such that the charged particle beam emitted by the charged beam source is irradiated on any one of the apertures formed on the first mask.
The present invention also provides a cell projection exposure-type charged particle beam drawing method in which a charged particle beam emitted by a charged particle beam source is irradiated for executing cell projection exposure onto a second mask comprising one or a plurality of cell projection exposure apertures through a first mask for exposing the pattern of the cell projection exposure apertures on a sample wafer, wherein the first mask comprises: a main aperture for exposing the whole area of the second mask for the cell projection exposure, and a supplementary aperture having a size of 1/N of the main aperture, wherein N is an integer; wherein most of a cell array pattern area on the sample wafer is exposed using a combination of the main aperture on the first mask and the cell projection exposure aperture on the second mask; and an excess cell array pattern area which occurs by exposing with the combination of the main aperture on the first mask and the cell projection exposure aperture on the second mask, is exposed using a combination of the supplementary aperture on the first mask and the partial exposure aperture on the second mask.
According to the above construction, the cell projection exposure aperture is 15 provided on the second mask and the main aperture through which the electron beam can be irradiated to the whole cell projection exposure aperture on the second mask and the supplementary aperture having a size of 1/N of the size of the main aperture are provided on the first mask, the center portion pattern of the cell array pattern is drawn by combining the cell projection exposure aperture and the main aperture, and further, the excess pattern of the cell array pattern is drawn by the cell projection exposure aperture. Therefore, the following effects are obtained:
(1) Since the size of the cell projection exposure aperture can be designed as big as possible within the size to be drawn using the drawing apparatus, the number of shots can be reduced.
(2) Since a part of the cell projection exposure aperture is chosen according to the supplementary aperture on the first mask, without depending on the deflector, the excess pattern can be drawn with high accuracy without depending on the deflection accuracy of the drawing apparatus.
(3) Since the positioning shift of the electron beam is not executed on the second mask, the interval between the adjacent apertures can be shortened and the number of the cell projection exposure apertures to be provided on the second mask can be increased.
(4) Since the center portion of the electron beam by which the masks are uniformly highly irradiated is preferably used instead of preferably using the end portion of the electron beam, the patterns can be satisfactorily formed without occurring a deterioration of the pattern shapes.